Annual change in pulmonary function and clinical phenotype in chronic obstructive pulmonary disease

Although the rate of annual decline in FEV1 is one of the most important outcome measures in chronic obstructive pulmonary disease (COPD), little is known about intersubject variability based on clinical phenotypes.

To examine the intersubject variability in a 5-year observational cohort study, particularly focusing on emphysema severity.

A total of 279 eligible patients with COPD (stages I-IV: 26, 45, 24, and 5%) participated. We conducted a detailed assessment of pulmonary function and computed tomography (CT) at baseline, and performed spirometry every 6 months before and after inhalation of bronchodilator. Smoking status, exacerbation, and pharmacotherapy were carefully monitored. Emphysema severity was evaluated by CT and annual measurements of carbon monoxide transfer coefficient.

Using mixed effects model analysis, the annual decline in post-bronchodilator FEV1 was -32±24 (SD) ml/yr (n=261). We classified the subjects of less than the 25th percentile as Rapid decliners, the 25th to 75th percentile as Slow decliners, and greater than the 75th percentile as Sustainers (-63±2, -31±1, and -2±1 [SE] ml/yr). Emphysema severity, but not %FEV1, showed significant differences among the three groups. Multiple logistic regression analysis demonstrated that the Rapid decliners were independently associated with emphysema severity assessed either by CT or carbon monoxide transfer coefficient. The Sustainers displayed less emphysema and higher levels of circulating eosinophils.

Emphysema severity is independently associated with a rapid annual decline in FEV1 in COPD. Sustainers and Rapid decliners warrant specific attention in clinical practice.